The present embodiments relate to an apparatus, medical imaging device, computer program product and/or a method for determining a movement phase of a moving object shown in a series of images. For example, methods and apparatuses of this type are used in medical imaging, since a reconstruction of three-dimensional images depends on the movement phase of the moving object (e.g., a lung) occurring while raw image data is being recorded.
Cone beam computed tomography is an example of a known medical imaging method. Cone beam computed tomography produces two-dimensional projections of the object using x-ray beams. The projections are produced using different angles from an angle range of over 180°. A three-dimensional image of the object may then be reconstructed from the two-dimensional projections.
Producing all of these two-dimensional projections from different directions is a time-consuming process. If the object (e.g., lung) to be imaged moves during this time (e.g., the lung executes a quasi-periodic, respiratory, movement), the individual projection image data items are produced in different phases of the object movement. If the projections are then used to reconstruct a three-dimensional image, the inconsistent projections may produce artifacts. Artifacts make it difficult to evaluate and/or diagnose the three-dimensional image.
One way of preventing such artifacts is only to use projections that correspond to the same respective movement phase of the moving object. For example, only projection images that correspond to the same respiratory position may be used for the reconstruction.
One way of determining the respiratory position is to use a respiration strap, as described in: Lars Dietrich et al, “Linac-integrated 4D cone beam CT: first experimental results,” 2006, Phys. Med. Biol. 51, 2939.
U.S. Pat. No. 7,349,564 discloses a method for determining the respiratory position of anatomical features, such as, for example, a diaphragm, in the image data.